The present invention relates to a printer having a bail roller opening and closing mechanism.
Printers are provided with a bail roller in order to hold continuous paper or cut sheets and the like against the platen in the vicinity of the printing head so that favorable printing operation can be performed.
In recent years, automatic paper loading system have been used, and accordingly printers have been required to provide bail roller opening and closing mechanisms to automatically shift the bail roller between a closed position where the bail roller is in contact with the platen and an open position where the bail roller is separated far from the platen.
These bail roller opening and closing mechanisms should desirably have a simple and highly reliable mechanism.
Conventionally, the motor for line feed is used as the drive power source for the opening and closing of the bail roller.
In mechanisms having this configuration, if bail roller opening and closing operation is performed while the paper is being loaded by the line feed motor, the load on the line feed motor changes while the paper is being loaded and discrepancies in the amount of line feed occur.
A bail roller opening and closing mechanism in which this problem has been eliminated is disclosed in Japanese Patent Laid Open Publication No.63-153170. In this mechanism, the configuration is such that the space motor that moves the printing head is used as the drive power source to rotate a cam to rotate an arm having a bail roller at its distal end.
In this mechanism, because the space motor is used, there occurs no adverse influence to the operation for loading the paper while performing opening and closing operation for the bail roller.
In addition, so that it is possible to rectify paper jams and the like, the configuration of the bail roller opening and closing mechanism must be such that the bail roller in the closed position can be moved manually to the open position.
In the mechanism disclosed in Japanese Patent Laid Open Publication No.63-153170, when the bail roller is pulled manually, the arm is rotated and the other end of the arm is separated from the cam surface of the cam. This is to say that the state where the cam and the arm have been in mechanical contact is cancelled. Accordingly, the cam enters the free state and can be easily rotated due to impact forces and the like.
If some impact force is applied to the printer while paper jam rectification is being carried out, and the cam then slips from its rotational position, there occurs some deviation between the actual rotational position of the cam and the predetermined rotational position of the cam, when the bail roller has been opened or closed. Because of this, the bail roller comes to be stopped before it reaches either the opened or the closed position, therefore preventing normal bail roller opening and closing operation from being carried out.